1. Field of the Invention
The present invention relates to a CPP (current perpendicular to the plane) type magnetic sensing element, and particularly to a magnetic sensing element permitting a decrease in the effective element size while maintaining the large optical element size, and permitting effective and easy improvement in reproduced output, and a method of manufacturing the same.
2. Description of the Related Art
FIG. 13 is a partial sectional view showing the structure of a conventional magnetic sensing element, as viewed from the side facing a recording medium.
In FIG. 13, reference numeral 1 denotes an underlying layer of Ta or the like, on which an antiferromagnetic layer 2 of PtMn or the like is formed. Furthermore, a pinned magnetic layer 3 made of NiFe or the like is formed on the antiferromagnetic layer 2, a nonmagnetic intermediate layer 4 made of Cu or the like is formed on the fixed magnetic layer 3, and a free magnetic layer 5 made of NiFe or the like is formed on the nonmagnetic intermediate layer 4. Also, a protecting layer 6 made of Ta or the like is formed on the free magnetic layer 5. A multilayer film 9 ranges from the underlying layer 1 to the protecting layer 6.
Magnetization of the pinned magnetic layer 3 is pinned in the Y direction shown in the drawing by an exchange anisotropic magnetic field with the antiferromagnetic layer 2.
Magnetization of the free magnetic layer 5 is oriented in the X direction shown in the drawing by a longitudinal bias magnetic field from each of hard bias layers 7 formed on both sides of the free magnetic layer 5 in the track width direction (the X direction shown in the drawing).
As shown in FIG. 13, electrode layers 8 are formed on the hard bias layers 7. The track width Tw is determined by the length of the upper surface of the free magnetic layer 5 in the track width direction (the X direction).
In the magnetic sensing element shown in FIG. 13, the direction of a current flow is referred to as a xe2x80x9cCIP (current in the plane) typexe2x80x9d in which the current flows in substantially parallel to the film plane of each of the layers of the multilayer film 9. This type is schematically shown in FIG. 14.
As shown in FIG. 14, in a multilayer film ranging from an antiferromagnetic layer to a free magnetic layer, the width of the upper surface of the free magnetic layer is the track width Tw, the thickness of the multilayer film is T, and the length of the multilayer film in the height direction (the Y direction shown in the drawing) is MRh.
When the current density (J=I/(MRhxc3x97T)) and the thickness T are constant, and the track width Tw and the height length MRh are reduced to 1/S, the resistance value R of the multilayer film is constant, and thus the change in resistance xcex94R is also constant. However, the sensing current I is reduced to 1/S, and thus output xcex94V (=xcex94Rxc3x97I) is also reduced to 1/S.
On the other hand, when the track width Tw and the height length MRh are reduced to 1/S with a constant heating value P, the resistance value R of the multilayer film is constant, and thus the change in resistance xcex94R is also constant. The sensing current I is also constant, and thus output xcex94V is a constant value.
In a CPP (current perpendicular to the plane) type magnetic sensing element in which the sensing current flows perpendicularly to the film plane of each of the layers of the multilayer film, the output xcex94V changes as follows:
FIG. 15 is a schematic drawing of a CPP type magnetic sensing element. Like in FIG. 14, in FIG. 15, the track width determined by the width of the upper surface of a free magnetic layer of a multilayer film is denoted by Tw, the thickness of the multilayer film is T, and the length of the multilayer film in the height direction (the Y direction shown in the drawing) is MRh.
Like in the CIP type, when the current density (J=I/(Twxc3x97MRh)) and the thickness T are constant, and the track width Tw and the height length MRh are reduced to 1/S, the resistance value R of the multilayer film is increased S2 times, and thus the change in resistance xcex94R is also increased S2 times. However, the sensing current I is reduced to 1/S2, and thus output xcex94V (=xcex94Rxc3x97I) is constant.
On the other hand, when the track width Tw and the height length MRh are reduced to 1/S with a constant heating value P, the resistance value R of the multilayer film is increased S2 times, and thus the change in resistance xcex94R is also increased S2 times. The sensing current I is reduced to 1/S, and thus output xcex94V is increased S times.
In this way, as narrowing of the element size advances, reproduced output V of the CPP type can be more increased than the CIP type. Therefore, the CPP type is expected to appropriately comply with narrowing of the element size with increases in the recording density in the future.
However, it was found that unless the track width Tw and the height length MRh are 0.1 xcexcm or less (i.e., the element area is 0.01 xcexcm2 or less), the CPP type magnetic sensing element cannot effectively produce higher reproduced output than the CIP type.
The element size will possibly gradually decrease with future increases in the recording density. However, with the accuracy of the present photolithography techniques, it is very difficult to form a magnetic sensing element having a 0.1 xcexcm square element area. Also, with an excessively small element size, a leakage magnetic field from a recording medium cannot be effectively sensed by the magnetic sensing element, thereby possibly causing deterioration in reproduced output and deterioration in stability of a reproduced waveform.
Accordingly, the present invention has been achieved for solving the above problem of the conventional technique, and an object of the present invention is to provide a magnetic sensing element permitting a decrease in the effective element size while maintaining the large optical element size, and permitting effective and easy improvement in reproduced output, and a method of manufacturing the magnetic sensing element.
The present invention provides a magnetic sensing element comprising a multilayer film comprising an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic intermediate layer and a free magnetic layer, wherein a current flows perpendicularly to the film plane of each of the layers of the multilayer film, and a current limiting layer comprising a mixture of an insulating portion and a conductive portion is provided on at least one of the upper and lower surfaces of the free magnetic layer directly or through another layer.
The magnetic sensing element of the present invention is a CPP type in which a sensing current flows perpendicularly to the film plane of each of the layers of the multilayer film.
Therefore, the sensing current perpendicularly flows in the current limiting layer. However, in the present invention, the current limiting layer provided on at least one of the upper and lower surfaces of the free magnetic layer comprises a mixture of the insulating portion and the conductive portion, and thus the sensing current flows only in the conductive portion.
Therefore, the sensing current flowing from an electrode layer to the free magnetic layer through the current limiting layer locally flows only in a portion of the free magnetic layer corresponding to the conductive portion to locally increase the current density in this portion.
Therefore, in the present invention, even when the element area (referred to as an xe2x80x9coptical element areaxe2x80x9d) of the free magnetic layer in the direction parallel to the film planes is formed in the same large size as a conventional element, the element area (referred to as an xe2x80x9ceffective element areaxe2x80x9d) in which the sensing current actually flows in the free magnetic layer to contribute to a magnetoresistive effect can be decreased. Thus, even when a magnetic sensing element having a large optical element size is formed by using a photolithography technique having the same degree of accuracy as conventional photolithography, a CPP type magnetic sensing element producing high reproduced output can easily be formed.
Also, the element size can be made the same as the conventional element, and thus the magnetic sensing element can effectively sense an external magnetic field from a recording medium, thereby permitting improvements in reproduced output and stability of a reproduced waveform.
In the present invention, the current limiting layer is preferably provided at least on the current arrival surface of the free magnetic layer directly or through another layer. This can appropriately narrow the path of the sensing current to decrease the effective element area, thereby permitting the manufacture of a CPP type magnetic sensing element producing high reproduced output.
In the present invention, the insulating portion of the current limiting layer preferably comprises an insulating material layer having a plurality of holes provided therein to pass through at least the current limiting layer, and the holes are preferably filled with a conductive material layer, which constitutes the conductive portion.
In the present invention, the insulating material layer preferably comprises an oxide film or a nitride film. The oxide film preferably comprises an insulating material composed of an oxide of at least one of Al, Si, Ti, Zr, Hf, Cr, Ta, V, Nb, Mo, W, Fe, Ni and Co.
The nitride film preferably comprises an insulating material composed of a nitride of at least one of Al, Si, Ti, Zr, Hf, Cr, Ta, V, Nb, Mo, W, Fe, Ni and Co.
Alternatively, the conductive portion of the current limiting layer preferably comprises conductive grains which are dispersed in an insulating material layer constituting the insulating portion.
For example, the current limiting layer preferably comprises a film structure in which microcrystal grains constituting the conductive portion and mainly composed of Fe are dispersed in an amorphous material constituting the insulating portion and containing a compound of O or N with at least one element M selected from Ti, Zr, Hf, Nb, Ta, Mo, W, and the rare earth elements.
In this case, the current limiting layer preferably has a composition represented by the formula FeaMbOc wherein the composition ratios a, b and c by atomic % are 40xe2x89xa6axe2x89xa650, 10xe2x89xa6bxe2x89xa630 and 20xe2x89xa6cxe2x89xa640, respectively, and satisfy the relationship a+b+c=100.
Alternatively, the current limiting layer preferably has a composition represented by the formula FedMeNf wherein the composition ratios d, e and f by atomic % are 60xe2x89xa6dxe2x89xa670, 10xe2x89xa6exe2x89xa615 and 19xe2x89xa6fxe2x89xa625, respectively, and satisfy the relationship d+e+f=100.
In the present invention, the insulating portion of the current limiting layer may comprise insulating grains dispersed in a conductive material layer constituting the conductive portion.
In the film structure of the current limiting layer, therefore, the insulating portion and the conductive portion can be appropriately mixed, thereby permitting an attempt to appropriately decrease the effective element size.
A method of manufacturing a magnetic sensing element of the present invention comprises the following steps:
(a) The step of depositing in turn a first electrode layer, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic intermediate layer and a free magnetic layer to form a multilayer film, and further depositing an insulating material layer on the free magnetic layer by sputtering, in which a plurality of holes are formed in the insulating material layer so as to pass through the insulating material layer.
(b) The step of depositing a conductive material layer on the insulating material layer by sputtering, in which the holes formed in the insulating material layer are filled with the conductive material layer.
(c) The step of forming a second electrode layer on a current limiting layer comprising the insulating material layer and the conductive material layer.
By these steps, the current limiting layer comprising the insulating material layer having a plurality of holes formed to pass through the insulating material layer, and the conductive material layer filling in the holes can be easily formed on the free magnetic layer.
In the present invention, in depositing the insulating material layer by sputtering in the step (a), the insulating material layer is preferably formed as a discontinuous film on the free magnetic layer. This enables the easy formation of a plurality of holes passing through the insulating material layer. In order to form the insulating material layer as the discontinuous film, the selection of the material and sputtering conditions are important. The sputtering conditions include a substrate temperature, Ar gas pressure, the distance between a substrate and a target, etc.
In the present invention, the insulating material layer is preferably deposited by sputtering an insulating material composed of an oxide of at least one of Al, Si, Ti, Zr, Hf, Cr, Ta, V, Nb, Mo, W, Fe, Ni and Co.
Alternatively, the insulating material layer is preferably deposited by sputtering an insulating material composed of a nitride of at least one of Al, Si, Ti, Zr, Hf, Cr, Ta, V, Nb, Mo, W, Fe, Ni and Co.
In another aspect of the present invention, a method of manufacturing a magnetic sensing element comprises the following steps:
(d) The step of depositing in turn a first electrode layer, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic intermediate layer and a free magnetic layer to form a multilayer film, and further depositing, on the free magnetic layer by sputtering, a current limiting layer having a composition represented by the formula FeaMbOc (wherein M is at least one element selected from Ti, Zr, Hf, Nb, Ta, Mo, W, and the rare earth elements) wherein the composition ratios a, b and c by atomic % are 40xe2x89xa6axe2x89xa650, 10xe2x89xa6bxe2x89xa630 and 20xe2x89xa6cxe2x89xa640, respectively, and satisfy the relationship a+b+c=100, and having a film structure in which microcrystal grains composed of Fe as a main component are dispersed in an amorphous material containing a compound of the element M and O.
(e) The step of forming a second electrode layer on the current limiting layer.
Alternatively, in the step (d), instead of FeaMbOc, a current limiting layer having a composition represented by the formula FedMeOf (wherein M is at least one element selected from Ti, Zr, Hf, Nb, Ta, Mo, W, and the rare earth elements) may be deposited by sputtering, in which the composition ratios d, e and f by atomic % are 60xe2x89xa6dxe2x89xa670, 10xe2x89xa6exe2x89xa615 and 19xe2x89xa6fxe2x89xa625, respectively, and satisfy the relationship d+e+f=100, and the current limiting layer has a film structure in which microcrystal grains composed of Fe as a main component are dispersed in an amorphous material containing a compound of the element M and N.
In the above manufacturing method, the current limiting layer can easily be formed on the free magnetic layer, in which the microcrystal grains composed of Fe as a main component are dispersed in the amorphous material containing an O or N compound with at least one element M selected from Ti, Zr, Hf, Nb, Ta, Mo, W, and the rare earth elements.
In the present invention, the multilayer film may be formed by depositing in turn a first electrode layer, a current limiting layer, a free magnetic layer, a nonmagnetic intermediate layer, a pinned magnetic layer and an antiferromagnetic layer.